1. Field of the Invention
The present invention relates to an interface of a monitor communicating with a personal computer (PC), and more particularly to an interface of a monitor which can input/output serial data through a printer port and a COM port simultaneously by providing a communication interface utilizing the printer port of the PC communicating with a microcomputer of the monitor, thereby improving communicability between the PC and the microcomputer of the monitor.
2. Description of the Related Art
As shown in FIG. 1, the conventional interface of a monitor communicating with a PC comprises a microcomputer 1 of the monitor for processing data by serial peripheral interface (SPI) communication, a printer port 3A, installed on the rear part of the PC 3, for inputting/outputting print data signals, and an interface section 2, connected between the printer port 3A and the microcomputer 1, for inputting/outputting data therethrough.
The interface section 2 comprises an inverter G1, connected between pin No. 2 of the printer port 3A of the PC 3 and a serial clock line (SCL) terminal of the microcomputer 1, for transmitting a clock line control signal, an inverter G2, connected between the SCL terminal of the microcomputer 1 and pin No. 15 of the printer port 3A of the PC 3, for checking the status of a clock signal transmitted from the inverter G1 to the microcomputer 1, an inverter G3, connected between pin No. 3 of the printer port 3A of the PC 3 and a serial data line (SDL) terminal, for transmitting a data line control signal, and a inverter G4, connected between the SDL terminal of the microcomputer 1 and pin No. 10 of the printer port 3A of the PC 3, for checking the status of data signal transmitted from the inverter G3 to the microcomputer 1.
The reference numberals R1 to R4 in FIG. 1 denote pull-up resistors.
The operation of the conventional interface of a monitor communicating with a PC will be explained.
First, in case that the PC 3 writes data into the microcomputer 1 through the clock line and the data line, the pin Nos. 2 and 3 of the printer port 3A of the PC 3 are initialized with `high` level signals. At an initial stage, as illustrated in FIG. 2A, the starting condition of the data transmission is given at the point where the clock line and the data line go from a `high` state to a `low` state. At this time, the microcomputer 1 acknowledges that the PC 3 starts data reading on writing operation by detecting the starting condition through the clock line and data line.
In case of writing the data in the microcomputer, the PC 3 outputs data through the inverter G3, synchronizing the data with the clock signal applied to the inverter G1 of the interface section 2. The microcomputer 1 of the monitor then receives and stores in a built-in memory the clock signal and the data inputted from the inverters G1, G3. Meanwhile, in case of reading the data from the microcomputer 1, the PC 3 reads necessary data through the inverters G2, G4 form the microcomputer 1.
At this time, the PC 3 feeds back the data and the clock signal outputted from the inverters G1, G3 through the inverters G2, G4 of the interface section 2 to check whether or not the current clock line and the data line operate in a normal state. Also, the PC 3 acknowledges the read data by recognizing the clock inputted/outputted through the inverter G3. Specifically, the PC 3 transmits or reads the data byte by byte by acknowledging the rising edge of the ninth clock of the clock signal. At this time, the microcomputer 1 of the monitor displays the inputted/outputted data on the monitor screen so that the user can see the data.
If the stop condition is inputted as shown in FIG. 2A during the above-described data input/output operation, the PC 3 terminates the data input/output operation.
However, according to the conventional interface of a monitor communicating with a PC, the PC cannot perform a data communication with the microcomputer through the printer port if the printer cable is connected to the printer port of the PC, thereby decreasing the usability of the system. Also, it is impossible to compatibly perform a serial communication or parallel communication using the input/output ports of the PC, thereby greatly deteriorating the operability of the system.